Hydraulic apparatus



Sept. 13, 1966 D. E. LAMBETH HYDRAULIC APPARATUS 2 Sheets-Sheet 1 Filed April 15, 1965 Dengis t f riw efh Sept. 13,1966 D. E. LAMBETH HYDRAULIC APPARATUS 2 Sheets-Sheet 2 Filed April 15, 1965 INVEMTO Dennis E. Lambe fh wilim m United States Patent 3,271,956 HYDRAULIC APPARATUS Dennis Ernest Lambeth, Cheltenham, England, assignor to Dowty Technical Developments Limited, Cheltenham, England, a British company Filed Apr. 15, 1965, Ser. No. 448,296 Claims priority, application Great Britain, Apr. 18, 1964, 16,185/64 Claims. (Cl. 6053) This invention relates to hydraulic apparatus and more particularly to a hydraulic power transmission which comprises a variable positive displacement hydraulic pump in hydraulic connection with a variable positive displacement hydraulic motor, the pump being adapted to receive power from a power source and the motor being adapted to deliver power to a load, the speed ratio between pump speed and motor speed being determined by the relative displacements of the pump and the motor.

The present invention is concerned with a hydraulic power transmission having the pump and the motor each of the tilting head kind and each comprising a rotary member secured to a drive shaft and a head tiltable about a tilt axis relatively to the rotary member. The head comprises a frame or casing containing a rotary cylinder block, a rotary drive means between the rotary member and the cylinder block and pistons associated with the cylinder block and arranged for reciprocation during ":0- tation of the rotary member. The tilt angle of the head relatively to the rotation axis of the rotary member determines the effective stroke of the pistons in their cylinders. A valve means containing a pair of ports is used for the supply and return flow of liquid to and from the cylinders. A pump or motor of the kind set forth in this paragraph will, for convenience be referred to hereafter as a tilting head pump unit or a til-ting head motor unit.

In accordance with the present invention a hydraulic transmission comprises a tilting head pump unit in hydraulic connection with a tilting head motor unit, a support locating the tilt axes and the drive shafts in fixed relative positions in which the tilt axes are parallel to one another, a link of fixed length having a pair of spaced pivots connecting the link respectively to the pump head and to the motor head, the pivots having axes parallel to the tilt axes and being attached to the heads either directly or through extensions whereby the spacing for each head between the tilt axis and the pivot axis forms a lever arm, the whole arrangement being such that during til-t movement of the heads a position is obtainable, referred to as pump dead centre in which the motor pivot axis lies between and in one plane with the pump tilt axis and the pump pivot axis.

Preferably stop or other limiting means are provided for the pump head which limit its range of movement such that the pivot axes can never enter into a position, known as a motor dead centre, in which th pivot axes lie in one plane with the motor tilt axis.

The transmission may be arranged in three basically different forms are follows:

(a) In the pump dead centre position, the pump lever arm makes an obtuse angle with the common plane through the tilt axes.

(b) In the pump dead centre position, the pump lever arm makes an acute angle with the common plane through the tilt axes and the pump lever arm is shorter than the tilt axis spacing.

(c) In the pump dead centre position the pump lever arm makes an acute angle with the common plane through the tilt axes and the pump lever arm is longer than the tilt axis spacing.

How the invention can be carried into effect is hereinafter particularly described with reference to the accompanying drawings in which,

FIGURE 1 illustrates one arrangement of the tilt and pivot axes according to the invention,

FIGURE 2 indicates diagrammatically one transmission based on the axis arrangement of FIGURE 1,

FIGURE 3 illustrates another arrangement of pivot and tilt axes according to the invention,

FIGURES 4 and 5 indicate diagrammatically two forms of transmission based on the arrangement of FIGURE 4,

FIGURE 6 illustrates a third arrangement of pivot and tilt axes according to the invention,

FIGURE 7 illustrates one transmission based on the axis arrangement of FIGURE 6, and

FIGURE 8 shows by way of example a cross section through a typical tilting head pump or motor unit used in the invention.

Initially reference is made to the tilting head unit illustrated in FIGURE 8. A drive shaft 13 is mounted for rotation within a fixed bearing housing 14 which is adapted by any convenient means to be fixedly secured in its operating position. The drive shaft 13 is integrally formed with a drive flange 15 which bears against a thrust bearing surface 16 formed on the housing 14. A pair of trunnions 17 are formed one on either side of the bearing housing 14, which trunnions are engaged by the arms 18 of a yoke 19. It will be understood that the yoke includes a pair of arms 18 disposed one on either side of the drive flange 15. The base 21 of the yoke 19 comprises a valve plate on which a cylinder block 22 is mounted for rotation. The cylinder block 22 is located in position on the valve plate by means of a fixed axle 23- secured to the valve plate 21. Within the cylinder block 22 a number of cylinders 24 are formed whose axes extend parallel to the axis of block rotation. These cylinders are open at the end of the cylinder block facing the drive flange 15. The end of the cylinder block 22 which co-operates with the valve plate 21 is formed with a number of cylinder ports 25 which extend one from each cylinder 24. The ports 25 co-operate with a pair of fixed ports 26 and 27 in the valve plate. Within each cylinder 24 a piston 28 is slidably mounted. Each piston is hollow and includes a connecting rod 29 secured Within the hollow portion and capable of limited angular movement in the piston. The connecting rods 29 extend from the pistons and terminate in ball joints 31. Each ball joint 31 is located within a socket member 32 fixed in the drive flange 15. The yoke 19 and cylinder block 22 being pivotally mounted at the trunnions 17 are capable of angular movement about the trunnion axis which is arranged to pass diametrically through the drive flange 15 through a circle on which the centres of the ball joints 3-1 are located. Assuming that the yoke is so positioned that the rotation axes of the cylinder block 24 and the drive shaft 13 are inclined to one another it will be seen that rotation of the drive shaft and rotation of the cylinder block will cause reciprocation of the pistons 28 within cylinders 24, one complete reciprocation of each piston being etfected for each complete revolution of the drive shaft 13. The ports 26 and 27 are so positioned that by rotation of the drive shaft 13 liquid is displaced from one of the ports 26 and 27 and delivered at the other port 26 or 27. Rotational drive of the cylinder block is obtained by virtue of the fact that the connecting rods 29 engage the interior surfaces of their associated pistons 28. The stroke of the pistons 28 Within their cylinders is determined by the angular inclination of the rotation axis of the cylinder block 22 to the rotation axis of the drive shaft 13, the greater the inclination the greater the stroke. At the position where the axes of the cylinder block 22 of the drive shaft 13 are aligned the pistons will have no stroke.

Extending from the yoke 19 is a lug 33 at the end of which a pair of swivel joints 34 are located. From the swivel joints 34 a pair of parallel links extend to the corresponding swivel joints of the other tilting head unit of the transmission. In FIGURES l to 7 the two parallel links are indicated as a single link 7. The two parallel links perform the hydraulic function of carrying flow and return liquid in between the two tilting head units for the transmission of power from the pump drive shaft to the motor drive shaft. The links also perform a mechanical function in that they link together the pump and the motor heads for simultaneous displacement adjusting movement.

Throughout the description of FIGURES l to 7 like reference numerals will refer to like parts of the transmission. Referring initially to FIGURE 1 the drawing is taken in a plane perpendicular to the four parallel major axes of the transmission which are as follows:

The pump tilt axis PT, the motor tilt axis MT, the pump pivot axis PP, the motor pivot axis MP. One transmission based on the axis arrangement of FIGURE 1 is diagrammatically illustrated in FIGURE 2. In this figure the pump drive shaft 3 and the pump tilting head 4 together form a tilting head pump unit whilst the motor drive shaft 1 and the motor tilting head 2 together form a tilting head motor unit. The transmission is mounted in a support (not shown) which provides bearing housings for the pump and motor drive shafts 3 and 1 and for the trunnions 5 and 6 of the motor and pump heads. The axes of the trunnions 5 and 6 form the tilt axes of the motor and pump heads, and are located at a fixed parallel relation in the support. A link 7 of fixed length is pivotally connected between the pivot positions MP and PP, the pivot MP being formed in a lug 8 extending from the motor head and the pivot PP being formed in a lug 9 extending from the pump head. As previously described the pump and motor heads each contain a rotary cylinder barrel having cylinders and connecting rods which are interconnected with the drive shaft such that during rotation of the drive shaft the pistons are reciprocated within the cylinders, the strokes of the pistons being proportional to the angular tilt of the head about the tilt axis. In the ease of the motor the spacing between the tilt axis MT and the pivot axis MP forms the motor lever arm whilst in the case of the pump the spacing between the tilt axis PT and the pivot axis PP forms the pump lever arm. If reference is made to FIGURE 1 it will be seen that a quadrilateral linkage is formed by the four sides of a quadrilateral whose corners are hinged together at the pivot and tilt axes. The four sides comprise the support between the tilt axes MT and PT, the pump lever arm, the motor lever arm and the link. As is well known with a quadrilateral linkage the sides are movable relatively to one another about their hinge connections without the lengths of the sides being altered and in the present invention use is made of this property of a quadrilateral linkage in order to control relative angular movement of motor and pump heads 2 and 4. In FIGURE 1 the motor and pump lever arms are of approximately equal length and are each shorter than the space between the tilt axes. The link is longer than the space between the tilt axes. In FIGURE 1 the full lines represent the position of the linkage at the pump dead centre position in which the pump lever arm is aligned with the link, i.e. the axes MP, PT and PP lie in one plane. In this position the motor lever arm is arranged to occupy a position corresponding to a maximum angular inclination to the motor drive shaft 1. This in turn corresponds to maximum displacement per revolution of the motor. In this position it is arranged that the angular position of the pump head corresponds to zero displacement of the pump per revolution. Means such as a servo motor 11 (FIGURE 2) are provided for adjusting the angular position of the pump head about the tilt axis PT and the servo motor 11 is so arranged that it can move the pump head over a limited angular range only, illustrated in FIGURE 1 by dotted lines representing the limits of position of the pump lever arm and the corresponding positions of the link and the motor arm. It will be seen that movement of the pump head in either direction from the pump dead centre position will result in angular movement of the motor head in one direction only which is arranged to cause reduction of the motor displacement per revolution.

In operation of the transmission shown in FIGURES l and 2 the pump drive shaft 3 is connected to a suitable power source and the motor drive shaft 1 is connected to a suitable load. In the pump dead centre position as shown in FIGURE 2, it is arranged that the zero displacement position of the pump head corresponds with the pump dead centre position and, therefore, in the position as shown, rotation of the pump drive shaft will cause no liquid to be delivered from the pump 4 and the motor will not rotate. By movement of the pump head slightly in one direction liquid will be delivered to the motor to cause it to rot-ate in one direction. If movement of the pump head were in the reverse direction the delivery from the pump to the motor would be reversed causing the motor drive shaft 1 to rotate in the opposite direction. One great advantage of the transmission illustrated lies in the fact that the relation between the pump and the motor displacements is non-linear and that movement of the pump head from its zero displacement position will initially cause only a very slight reduction of motor displacement. For small pump head angular movements the pressure generated by the pump will lie at a maximum and since the motor will remain substantially at maximum displacement a maximum torque will be developed at the motor drive shaft. Large angular movements of the pump head from the zero displacement position will cause substantial reduction of the displacement of the motor head and the motor may be driven at a substantial speed having regard to the pump speed.

The important characteristics of the transmission of FIGURES l and 2 are that in the dead centre pump position firstly the motor pivot axis MP lies between the pump tilt axis PT and the pump pivot axis PP and secondly that the pump lever arm makes an obtuse angle with the plane through the tilt axes MT and PT.

Reference is now made to FIGURE 3 of the accompanying drawings which shows a second relative arrangement of pivot and tilt axes. The characteristic features of FIGURE 3 are that in the pump dead centre position firstly, the motor pivot axis MP lies in between the pump pivot axis PP and the pump tilt axis PT, secondly that the pump lever arm makes an acute angle with the common plane through the tilt axes MT and PT and thirdly that the pump lever arm is shorter than the space between the tilt axes MP and PT.

FIGURE 4 illustrates one form of transmission based on the axis arrangement of FIGURE 3. In this arrangement the pump and motor drive shafts are parallel and extend in the same direction from the transmission.

For each of the axis arrangements shown it is possible to design a number of varying forms of transmissions. By way of example FIGURE 5 illustrates a further transmission based on the FIGURE 3 arrangement of axes in which the pump and motor drive shafts 3 and I extend from the transmission in directions at right angles to one another.

The operation of the transmissions shown in FIG- URES 4 and 5 are each substantially as described for FIGURE 2.

Reference is now made to the axis arrangement shown in FIGURE 6. The characteristic features of this arrangement are that in the pump dead centre position firstly the motor pivot axis MP lies in between the pump pivot axis PP and the pump tilt axis PT, and secondly that the pump lever arm makes an acute angle with the plane passing through the tilt axes MT and PT. Further the pump lever arm is longer than the spacing between the tilt axes MT and PT.

FIGURE 7 illustrates a transmission based on the axis arrangement of FIGURE 6. This transmission is arranged so that the pump and motor drive shafts 3 and. 1 are inclined to one another.

In all the transmissions in FIGURES 2, 4, 5 and 7 the servo motor 11 is so arranged that it will determine the limits of angular movement of the pump head 4 in both the forward and the reverse directions. In modifications of the basic axis arrangement of FIGURES 1, 4 and 6, it might be possible within the limits of movement imposed on the pump head for movement of the heads and the link to occur which permit the link pivots tolie in one plane with the motor tilt axis. This would give a motor dead centre position which will effectively lock the heads and the links against movement by the single servo motor 11. Whilst it is desirable to be able to adjust the transmission through its complete range of adjustment i.e. from maximum forward to maximum reverse pump displacement by means of one servo motor it may on occasions be necessary to design the transmission to obtain certain characteristics which require that the transmission should pass through a motor dead centre position. In this case it would be within the scope of the invention to provide a further servo motor acting on the motor head and energised in conjunction with the pump servo rotor to move the transmission through the motor dead centre position.

In the illustrated transmissions the links 7 in each case may take the form of two hollow parallel links which in addition to the function of controlling relative movements of pump and motor heads also serve to carry flow or return liquid between the pump and the motor heads. Where such parallel links are provided they may extend one on either side of the pump head from the pump pivot. Where the link solely controls the relative pump and motor head positions, the hydraulic connections between the pump and motor heads may take any convenient form, and may extend for example between the pump and motor head trunnions.

In all of the transmissions shown in FIGURES 2, 4, 5 and 7 the pump has been arranged to occupy its zero displacement position when in the pump dead centre position. This arrangement need only be used where approximately equal forward and reverse speed ratios are desired through the transmission.

If it is desired for example that the forward speed ratio should be considerably greater than the reverse speed ratio it might be desirable to arrange that the pump zero displacement position is spaced by few degrees of angle from the pump dead centre position.

I claim:

1. A hydraulic power transmission comprising a tilting head pump unit in hydraulic connection with a tilting head motor unit, a support locating the tilt axes and the drive shafts in fixed relative positions in which the tilt axes are parallel to one another, a link of fixed length having a pair of spaced pivots connecting the link respectively to the pump head and to the motor head, the pivots having axes parallel to the tilt axes and being attached to the heads either directly or through extensions whereby the spacing for each head between the tilt axis and the pivot axis forms a lever arm, the whole arrangement being such that during tilt movement of the heads a position is obtainable, referred to as pump dead centre, in which the motor pivot axis lies between and in one plane with the pump tilt axis and the pump pivot axis.

2. A hydraulic power transmission as claimed in claim 1 including stop means for the pump head which limit its range of movement such that the pivot axes can never enter into a position known as the motor dead centre position, in which the pivot axes lie in one plane with the motor tilt axis.

3. A hydraulic power transmission as claimed in claim 1 wherein at the pump dead centre position the pump lever arm makes an obtuse angle with the common plane through the tilt axes.

4. A hydraulic power transmission as claimed in claim 1 wherein at the pump dead centre position, the pump lever arm makes an acute angle with the common plane through the tilt axes and the pump lever arm is shorter than the tilt axis spacing.

5. A hydraulic power transmission as claimed in claim 1 wherein at the pump dead centre position the pump lever arm makes an acute angle with the common plane through the tilt axes and the pump lever arm is longer than the tilt axis spacing.

References Cited by the Examiner UNITED STATES PATENTS 3,142,963 *8/1964 Thoma 53 3,142,964 8/1964 Thoma 6053 3,143,859 8/1964 Thoma 60-53 3,163,987 l/1965 Dowty et al. 6053 3,213,619 '10/ 1965 Creighton et al 60-53 FOREIGN PATENTS 962,361 7/ 1964 Great Britain. 693,320 8/1964 Canada.

EDGAR W. GEOGHEGAN, Primary Examiner. 

1. A HYDRAULIC POWER TRANSMISSION COMPRISING A TILTING HEAD PUMP UNIT IN HYDRAULIC CONNECTION WITH A TILTING HEAD MOTOR UNIT, A SUPPORT LOCATING THE TILT AXES AND THE DRIVE SHAFTS IN FIXED RELATIVE POSITIONS IN WHICH THE TILT AXES ARE PARALLEL TO ONE ANOTHER, A LINK OF FIXED LENGTH HAVING A PAIR OF SPACED PIVOTS CONNECTING THE LINK RESPECTIVELY TO THE PUMP HEAD AND TO THE MOTOR HEAD, THE PIVOTS HAVING AXES PARALLEL TO THE TILT AXES AND BEING ATTACHED TO THE HEADS EITHER DIRECTLY OR THROUGH EXTENSIONS WHEREBY THE SPACING FOR EACH HEAD BETWEEN THE TILT AXIS AND THE PIVOT AXIS FORMS A LEVER ARM, THE WHOLE ARRANGEMENT BEING SUCH THAT DURING TILT MOVEMENT OF THE HEADS A POSITION IS OBTAINABLE, REFERRED TO AS PUMP DEAD CENTRE, IN WHICH THE MOTOR PIVOT AXIS LIES BETWEEN AND IN ONE PLANE WITH THE PUMP TILT AXIS AND THE PUMP PIVOT AXIS. 